Commit facd15df authored by Johannes Berg's avatar Johannes Berg Committed by Jakub Kicinski
Browse files

net: core: synchronize link-watch when carrier is queried 

There are multiple ways to query for the carrier state: through
rtnetlink, sysfs, and (possibly) ethtool. Synchronize linkwatch
work before these operations so that we don't have a situation
where userspace queries the carrier state between the driver's
carrier off->on transition and linkwatch running and expects it
to work, when really (at least) TX cannot work until linkwatch
has run.

I previously posted a longer explanation of how this applies to
wireless [1] but with this wireless can simply query the state
before sending data, to ensure the kernel is ready for it.

[1] https://lore.kernel.org/all/346b21d87c69f817ea3c37caceb34f1f56255884.camel@sipsolutions.net/



Signed-off-by: default avatarJohannes Berg <johannes.berg@intel.com>
Reviewed-by: default avatarJiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20231204214706.303c62768415.I1caedccae72ee5a45c9085c5eb49c145ce1c0dd5@changeid


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent faf4cf74

include/linux/netdevice.h

+9 −0
Original line number Diff line number Diff line
@@ -4229,6 +4229,15 @@ static inline void netdev_ref_replace(struct net_device *odev, 
 */

void linkwatch_fire_event(struct net_device *dev);



/**

 * linkwatch_sync_dev - sync linkwatch for the given device

 * @dev: network device to sync linkwatch for

 *

 * Sync linkwatch for the given device, removing it from the

 * pending work list (if queued).

 */

void linkwatch_sync_dev(struct net_device *dev);



/**

 *	netif_carrier_ok - test if carrier present

 *	@dev: network device

net/core/dev.c

+1 −1
Original line number Diff line number Diff line
@@ -10548,7 +10548,7 @@ void netdev_run_todo(void) 
		write_lock(&dev_base_lock);

		dev->reg_state = NETREG_UNREGISTERED;

		write_unlock(&dev_base_lock);

		linkwatch_forget_dev(dev);

		linkwatch_sync_dev(dev);

	}



	while (!list_empty(&list)) {

net/core/dev.h

+0 −1
Original line number Diff line number Diff line
@@ -30,7 +30,6 @@ int __init dev_proc_init(void); 
#endif



void linkwatch_init_dev(struct net_device *dev);

void linkwatch_forget_dev(struct net_device *dev);

void linkwatch_run_queue(void);



void dev_addr_flush(struct net_device *dev);

net/core/link_watch.c

+1 −1
Original line number Diff line number Diff line
@@ -245,7 +245,7 @@ static void __linkwatch_run_queue(int urgent_only) 
	spin_unlock_irq(&lweventlist_lock);

}



void linkwatch_forget_dev(struct net_device *dev)

void linkwatch_sync_dev(struct net_device *dev)

{

	unsigned long flags;

	int clean = 0;

net/core/net-sysfs.c

+7 −1
Original line number Diff line number Diff line
@@ -194,8 +194,14 @@ static ssize_t carrier_show(struct device *dev, 
{

	struct net_device *netdev = to_net_dev(dev);



	if (netif_running(netdev))

	if (netif_running(netdev)) {

		/* Synchronize carrier state with link watch,

		 * see also rtnl_getlink().

		 */

		linkwatch_sync_dev(netdev);



		return sysfs_emit(buf, fmt_dec, !!netif_carrier_ok(netdev));

	}



	return -EINVAL;

}